Oil question....

[Upatdawn]

Does engine oil get thinner or thicker with use?

is there a difference in the state of oil after 20,000 miles between a petrol engine and a diesel engine?

[Upatdawn]

i meant, after (say) 15,000 miles is engine oil thinner or thicker than when new

and which gets thinner faster, petrol engine oil or diesel engine oil?

[Upatdawn]

Pumaracing said:

There are two opposing mechanisms at work here. Over time the long chain polymer molecules that help give a multigrade oil its high temperature viscosity get chopped up by the oil pump gears, piston rings etc and the oil loses viscosity.

However contamination from soot, other by-products of combustion and wear particles increase viscosity and this is by far the biggest factor, especially in a diesel engine. So generally viscosity increases with mileage.

so it gets thinner?

[Upatdawn]

Pumaracing said:

Are you taking the piss after everything I've written above?

No, you said "with mileage the viscosity increases"

im afraid im am but a poor and simple simpleton mate, that might easily mean anything

sorry